The detaching rollers of a combing machine carry out, as is known, two rotational movements which are related to each other in a certain way, namely one in the forward direction in order to separate the combed fiber tuft from a breaker lap and supply it to the take-off roll, and one in the backwards direction in order to deliver back the fiber which needs piecing. It is known to produce this pilgrim step motion (rotating the detaching rollers about twice as far forward as backwards) of the detaching rollers by superimposing a circular and a reciprocating rotational movement using planet wheel differentials. In one device provided with a differential arrangement which is simple in its constructional aspect, the reciprocating movement is produced by means of a preceding cam gear, and is then fed to the planet wheel, (German Auslegeschrift No. 1 008 624).
In the case of higher machine speeds, where the trend for combing machines lies, such a grooved cam gear is however, not suitable because of the unsuitable frictional and tolerance relationships. Furthermore, changing the nature and size of the movement of the detaching rollers is complicated and takes time, since in order to do this, the guide cam in the pinion on the drive shaft has to be changed.
A camless gearing such as disclosed in German Auslegeschrift No. 1 008 624 is relatively expensive compared with the above devices. Furthermore, it needs additional gear members, which among other things, cooperate with each other in two sliding fulcrum pairs and with other gear members. This leads to increased sliding friction, lubrication problems and increased wear. For fast running combing machine, this solution is hence unfavorable.
As already known, a planet wheel differential gear with two planet wheels is also expensive from a constructional point of view since the planet wheels are provided with a to-and-fro reciprocating movement from a crank gear (German Patent No. 237 375). A change of the crank radius and hence the highest values of the reciprocating speed which is imposed on the steady speed is possible with this gearing only coarsly using predetermined steps provided by holes in the crank disk.